Although the prior art has recognized the desirability of plastic-surfaced sucker rods as in Brown U.S. Pat. No. 3,212,582 for purposes of reducing paraffin build-up on such sucker rods, the art has not suggested the use of a partially plastic, glass-reinforced sucker rod construction for purposes of providing superior strength as well as superior operating characteristics.
In accordance with one embodiment of this invention, a novel rod construction comprising a core of high tensile material such as 4130 steel is embedded within an outer shell of glass filament-reinforced cured resin. The tensile strength provided by the shell provides the composite rod construction with excellent tensile strength and flexing characteristics, although lighter in weight than a steel rod of comparable size. The provided rod, in addition to the exceptional strength characteristics, possesses the corrosion resistance of a chemically inert resin, a most desirable characteristic when employed in oil field operations.
It is an object of this invention, therefore, to provide a novel, composite rod construction comprising a high tensile steel core encapsulated in a cured resin shell reinforced by glass filaments.
It is a further object of this invention to provide a reinforced sucker rod construction having a superior flexural modulus, of optimum weight which is of less weight than a rod of solid steel so as to minimize energy consumption in the course of pump operation while being of adequate weight so as to allow efficient insertion into a well tubing in the absence of excessive flexing and "floating."
It is another object of this invention to provide a rod construction having shear-resistant threads integrally formed in a female coupling end by use of a novel reinforcing band embedded in said end. Such threads may also be formed in a discrete coupling member adapted to engage the pin ends of joined rods.
It is a further object of this invention to provide a novel method of forming a sucker rod construction in which the excellent tensile strength of glass is employed to contribute to the overall tensile strength of the rod construction.
It is another object of this invention to provide a novel rod construction consisting of longitudinal and spiral layers of glass filaments under tension embedded in a matrix of cured resin which is of exceptional tensile strength and corrosion resistance and particularly adapted for use in applications requiring such desired properties as well as light weight.
The above and other objects of this invention will become apparent from the following detailed discussion when read in the light of the accompanying drawing and appended claims.
In one embodiment of this invention a longitudinal assemblage of glass roving strands is positioned about the periphery of a high tensile steel core, parallel to the core axis and placed under tension. The glass filaments comprising the strands are preferably untwisted to eliminate self-cutting action thereof. The steel rod or bar comprises the core of a composite rod construction in which a cured resin shell is disposed about the entire outer core periphery.
The steel core may be threaded or provided with regularly spaced annular indentations disposed along the core axis and arranged substantially normal to said axis. The glass filament or strand assemblage is locked adjacent opposed ends of the core while in the tensioned state, and saturated with a hardenable epoxy resin composition. With the resin in the uncured state, spiral windings of resin-saturated glass roving are wound along the core length so as to urge the longitudinal glass filaments into the surface indentations.
Additional layers of resin-saturated longitudinal strands and spiral windings are applied to the core until a rod of desired dimensions is formed. The resin is then cured at desired curing temperatures, care being taken during the cure to avoid separation or delamination between the core and the surrounding resin jacket. In accordance with this invention each spiral filament layer comprises two strata of filaments wound under tension about the underlying, rotating rod core portion, with the tension imparted by each layer spiral component being neutralized by the other spiral component as will hereinafter be explained in greater detail.
Resin male teeth may be formed about the external periphery of one completed rod end by means of an appropriate male thread mold. A reinforcing metal band may be centrally embedded in the resin shell at the opposed coupling rod end having female threads therein. Such teeth may be formed adjacent the inner periphery of the reinforcing band by means of a female thread mold as will hereinafter be explained in greater detail.
In an embodiment of a rod construction formed in accordance with this invention, the core reinforcement above described is omitted and the rod consists of tensioned longitudinal spiral filament layers embedded in a resin matrix. The innermost center "core" or layer of such a rod comprises longitudinal resin-saturated filaments under tension rotated as a unit and about which are wound resin-saturated spiral filaments under tension. The spirals are wound simultaneously in such a manner whereby the tensions on the rotating, partially formed rod portion exerted by the spiral filaments offset each other, resulting in a straight rod construction of high tensile strength and corrosion resistance.